Section 2.3—Chemical Formulas

We need to be able to read the formulas for chemicals in the antacids!

Your Appendix (Page A-2) has lists of: Common polyatomic ions Multivalent metals Covalent prefixes

Use your periodic table to determine the charges of common elements when they form ions

Reminders from Section 2.2

Binary Ionic compounds

Definitions

Binary Ionic Compound- compound containing two elements—one metal and one non-metal

+Cation

-Anion Ionic Compound

Ionic bond- bond formed by attraction between + and - ions

Metals & Non-MetalsIonic Bonds are between metals & non-metals

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra Lr Rf Db Sg Bh Hs Mt Uun Uuu Uub Uut

Metals Metalloids Non-metals

These compounds: End in “-ide” (except “hydroxide and cyanide”) Do NOT contain covalent prefixes

To write these formulas: Write the symbol & charge of the first element (the metal,

cation) Write the symbol & charge of the second element (the

non-metal, anion) Add more of the cations and/or anions to have a neutral

compound Use subscripts to show how many of each type of ion is

there.

Identifying & Naming Binary Ionic

Example #1

Sodium chloride

Example #1

Sodium chloride

Cation

Anion

Na+1

Cl-1

NaCl

Example #1

Sodium chloride

Cation

Anion

Na+1

Cl-1

NaCl

Na+1Cl-1

+1 + -1 = 0

The compound is neutral…no subscripts are needed.

Example #2

Calcium bromide

Example #2

Calcium bromide

Cation

Anion

Ca+2

Br-1

Example #2

Calcium bromide

Cation

Anion

Ca+2

Br-1

CaBr2

Ca+2Br-1

+2 + -1 = +1

Ca+2Br-1Br-1

The subscript “2” is used to show that 2 anions are needed.

+2 + -1 + -1 = 0

Let’s Practice

Example:Write the following chemical formulas

Cesium chloride

Potassium oxide

Calcium sulfide

Lithium nitride

Let’s Practice

CsCl

K2O

CaS

Li3N

Example:Write the following chemical formulas

Cesium chloride

Potassium oxide

Calcium sulfide

Lithium nitride

Polyatomic Ionic Compounds

Definition

Polyatomic Ion- more than one atom that together have a charge

+Cation

Polyatomic Ionic Compound- compound containing at least one polyatomic ion

-Polyatomic

AnionPolyatomic Ionic

Compound

These compounds: Do not end with “-ide” (except hydroxide & cyanide) Do not use covalent prefixes

To write these formulas: Write the symbol & charge of the cation & anion Add additional cations or anions to have a neutral

compound Use subscripts to show the number of ions

When using subscripts with a polyatomic ion, you must put the polyatomic ion in parenthesis.

Identifying & Naming Polyatomic Ionic

Example #3

Sodium carbonate

Example #3

Sodium carbonate

Cation

PolyatomicAnion

Na+1

CO3-2

Example #3

Sodium carbonate

Cation

PolyatomicAnion

Na+1

CO3-2

Na2CO3

Na+CO32-

+1 + -2 = -1

Na+Na+CO32-

The subscript “2” is used to show that 2 cations are needed.

+1 + 1 + -2 = 0

Example #4

Magnesium nitrate

Example #4

Magnesium nitrate

Cation

PolyatomicAnion

Mg+2

NO3-1

Example #4

Magnesium nitrate

Cation

PolyatomicAnion

Mg+2

NO3-1

Mg(NO3)2 Use parenthesis when adding subscripts to polyatomic ions

Mg+2NO3-

+2 + -1 = 1

Mg+2NO3- NO3

-

The subscript “2” is used to show that 2 anions are needed.

+2 + -1 + -1 = 0

Let’s Practice

Example:Write the following chemical formulas

Sodium nitrate

Calcium chlorate

Potassium sulfite

Calcium hydroxide

Let’s Practice

NaNO3

Ca(ClO3)2

K2SO3

Ca(OH)2

Example:Write the following chemical formulas

Sodium nitrate

Calcium chlorate

Potassium sulfite

Calcium hydroxide

Multivalent Metals

Definition

Multivalent Metal- metal that has more than one possibility for cationic charge

These compounds: Will have roman numerals

To write these formulas: Same as binary ionic or polyatomic ionic. The roman numerals tell the charge of the

metal (cation)

Identifying & Naming Multivalent Metals

Example #5

Iron (III) oxide

Example #5

Iron (III) oxide

Cation

Anion

Fe+3

O-2

Example #5

Iron (III) oxide

Cation

Anion

Fe+3

O-2

Fe2O3

Fe+3O2-

+3 + -2 = -1

Fe+3Fe+3O2-O2-

The subscript “2” and “3” are used to show the numbers of atoms needed.

+3 + 3 + -2 + -2 + -2 = 0

Example #6

Copper (II) nitrate

Example #6

Copper (II) nitrate

Cation

PolyatomicAnion

Cu+2

NO3-1

Example #6

Copper (II) nitrate

Cation

PolyatomicAnion

Cu+2

NO3-1

Cu(NO3)2

Cu+2NO3-

+2 + -1 = 1

Cu+2NO3-NO3

-

Use parenthesis when adding subscripts to a polyatomic ion

+2 + -1 + -1 = 0

Let’s Practice

Example:Write the following chemical formulas

Iron (II) nitrate

Copper (I) chloride

Lead (IV) hydroxide

Tin (II) oxide

Let’s Practice

Fe(NO3)2

CuCl

Pb(OH)4

SnO

Example:Write the following chemical formulas

Iron (II) nitrate

Copper (I) chloride

Lead (IV) hydroxide

Tin (II) oxide

Binary Covalent Compounds

Definition

Binary Covalent Compound compound made from two non-metals that share electrons

Nonmetal

Nonmetal Covalent compound

Covalent bond atoms share electrons

These compounds: Use covalent prefixes

To write these formulas: Write the symbols of the first and second

element Use the covalent prefixes (assume the first

element is “1” if there’s no prefix) as the subscripts to show number of atoms.

Identifying & Naming Binary Covalent

Atoms do not form charges when bonding covalently…you DO NOT need to worry about charges with this type!

Example #7

Dinitrogen Tetraoxide

Example #7

Dinitrogen Tetraoxide

N

O

“Di-” = 2

“Tetra-” = 4

N2O4

Example #8

Silicon dioxide

Example #8

Silicon dioxide

Si

O

“Mono-” is not written for the first element

“Di-” = 2

SiO2

CAUTION!!!

bi-di-

Stands for “2” in covalent compounds

Means there’s a hydrogen in the polyatomic anion

“di” and “bi” do not mean the same thing!

Carbon dioxide = CO2Sodium biphosphate =

Na2HPO4

Let’s Practice

Example:Write the following chemical formulas

Carbon monoxide

Nitrogen dioxide

Diphosphorus pentaoxide

Let’s Practice

CO

NO2

P2O5

Example:Write the following chemical formulas

Carbon monoxide

Nitrogen dioxide

Diphosphorus pentaoxide

Nomenclature Summary

Writing Chemical Formulas

Does not contain covalent prefixes

Does contain covalent prefixes = Binary

Covalent compound

Ends with “-ide” (except hydroxide &

cyanide) = Binary Ionic

All others = Polyatomic Ionic

Mixed Practice

Example:Write the following chemical formulas

Magnesium hydroxide

Copper (II) nitrate

Iron (III) oxide

Nitrogen dioxide

Sodium bicarbonate

Mixed Practice

Mg(OH)2

Cu(NO3)2

Fe2O3

NO2

NaHCO3

Example:Write the following chemical formulas

Magnesium hydroxide

Copper (II) nitrate

Iron (III) oxide

Nitrogen dioxide

Sodium bicarbonate